Apparatus and method for engine performance evaluation

ABSTRACT

A system that measures the density of the air in the intake of an internal combustion engine and calculates the gain or loss in performance provides a display to an operator in real time in a single, quickly assimilated reading. A display can indicate the combined power increasing effects of turbo/superchargers that increase density and power by compressing the air, as well as charge air coolers that increase density by decreasing the temperature. Density can be measured directly, or calculated from sensor readings. Densities, as well as temperatures and pressures can be displayed as absolute values, as percentage gains or losses verses a known reference such as ambient, or as a loss or gain between density increasing devices to indicate the individual performance of the component. One embodiment incorporates a cradle mounted PDA type handheld computing device on the dashboard to provide the display, input/output and processing hardware.

STATEMENT OF RELATED APPLICATIONS

This application claims priority from Provisional Application Ser. No.60/663,021, filed Mar. 17, 2005, the disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

The field of the present invention is measurement of engine performance.

Internal combustion engines produce power by using the oxygen in air toburn fuel to produce heat, which is then converted into mechanicalpower. The primary factor controlling the maximum available power levelof any given internal combustion engine is the amount of air (andtherefore oxygen) that is available to burn fuel. Since burning fuel isa chemical reaction, there are appropriate ratios of the number ofoxygen molecules needed to burn the fuel molecules present with optimumcombustion efficiency and minimum harmful exhaust byproducts.

The volume of air available is not alone determinative of how manyoxygen molecules will be present. How closely the molecules are packedinto this volume, density, must also be measured. Density is measured asmass of air divided by the volume occupied by that mass of air. For“ideal gasses” like air, this relationship is defined by the Ideal GasLaw as PV=nRT. In this equation, P is pressure, V is volume, n is thenumber of molecules, R is a constant depending on the units used, and Tis temperature. This can be algebraically rearranged to nR/V=P/T. Thisshows that to increase the number of molecules of air (n) in a fixedvolume (V), you must either increase the pressure (P), or decreasetemperature (T), or do both. This relationship additionally explains whythe power output of internal combustion engines, particularly thosewhich are normally aspirated, are affected by the prevailing ambient airconditions of temperature and barometric pressure, as this determinesthe maximum available intake air density, and therefore the maximumpower.

Another factor impacting the number of oxygen molecules is a variationin the constituent mixture of air. Humidity is the only significantnatural variable in the constituent mixture as applied to conventionallyemployed engines. By contributing water molecules to the mixturedefining ambient air, humidity has an impact on the percentage of themix which is oxygen. The influence of humidity is not reflected in theIdeal Gas Law but, when the water remains in a gaseous state, humid airmixture also can be considered to conform to the ideal gas model. Albeitimpacting on engine performance, humidity is usually not controlled orcontrollable in internal combustion engines.

The intake air density can be intentionally changed to control the poweroutput. A spark ignition (SI or Otto cycle) internal combustion engineuses changes in intake air density as the primary means for controllingpower output levels. This method is somewhat unique to SI enginesbecause they must operate within a relatively narrow range of allowableair/fuel ratios. They are unable to reduce power output, for example, bysimply restricting the fuel input while running with excess air as can acompression ignition (CI or Diesel cycle) engine. SI engines typicallylimit power by lowering the engine intake air density below ambientpressure with a throttle. This is a valve located in the intake airtract that generates an adjustable pressure drop in the flow of intakeair as it is closed, thereby controllably decreasing the density and,therefore, the power level.

At maximum power, normally aspirated SI and CI engines face the samelimitation: they cannot burn more fuel than the amount of oxygenavailable in air at existing atmospheric pressures and temperatures.Modern high performance engines frequently employ devices to increasethe available engine power beyond this limitation by compressing theintake air to increase its density. This is commonly accomplished withdevices called turbochargers or superchargers.

Unfortunately, compressing air causes an increase in the airtemperature. Looking again at the Ideal Gas Law, an increase intemperature adversely affects density. However, the temperature of thecompressed air is now above ambient, creating an opportunity for easilytransferring heat and thereby further increasing density and theobtainable power. Temperature reduction can be accomplished with heatexchange devices commonly called charge air coolers and intercoolers

Thus, mechanisms are available for modifying the limitations on SI andCI engines. Resulting density is a principal factor in the effectivenessof such modifications.

Various devices are known to monitor and control certain enginefunctions. Devices to indicate power level for engines usingturbochargers or superchargers are known which measure the intakemanifold pressure. These are commonly called “boost” gauges as theymeasure the additional pressure above atmospheric provided by theturbocharger or supercharger to “boost” the power output. Some versionsalso indicate pressure below atmospheric as a manifold vacuum gauge foran SI engine, or both above and below sea level ambient as in anaircraft manifold “absolute pressure” gauge. This gives the operator ofan SI engine at full throttle or a CI engine at the maximum fuel settinga rough indication of the effectiveness of the boost device and of itsrelative impact on power produced.

Devices to measure manifold temperatures are also available. These canmeasure the effectiveness of an intercooler or reflect adverse engineconditions. They do not provide any measure of engine performance.

The equivalent of density measurements are available for use forinternal engine control. Many modern computer controlled SI enginesmeasure both intake manifold air temperature and pressure for use indetermining the amount of fuel that is required to achieve the optimumair/fuel ratio. They do not, however, make this information available tothe operator. Density measurements are unknown for application as ameans for indicating component and system performance or power levels tothe operator of the internal combustion engine.

Some CI systems indicate engine “load” based on the quantity of fuelsupplied. They cannot sense when ambient conditions, or a systemmalfunction or degradation is limiting available air density, impactingpower.

Personal Digital Assistants (PDA) or similar small hand held computersare used with engines to compute or display engine or vehicle data. Suchdevices principally have been diagnostic tools to measure various engineparameters and signals which do not provide an indication of overallperformance.

SUMMARY OF THE INVENTION

The present invention is directed to a system for indicating theperformance of an internal combustion engine, including method andapparatus. An air density sensor is disposed in the intake of aninternal combustion engine and produces an output signal that is afunction of the density of the air in the intake. A display is incommunication with the air density sensor.

In a first separate aspect of the present invention, the displaydisplays the output signal in units which may be one or more of density,density divided by a predetermined value, percent density gain or loss,power output, power output divided by a predetermined value and poweroutput gain or loss.

In a second separate aspect of the present invention, an air densitysensor is used which includes a gas tight flexible container with gasdisposed therein and a pressure sensor to generate the output signal.The gas is provided in a predetermined quantity selected to produce apressure within the flexible container that is a function of the densityof the air in the internal combustion engine intake.

In a third separate aspect of the present invention, the air densitysensor includes a pressure sensor and a temperature sensor to generatethe output signal. The pressure sensor and the temperature sensor are inclose physical proximity within the intake.

In a fourth separate aspect of the present invention, the output signalis an electrical signal and the display includes a converter which maybe a digital processor and may, more specifically, be a PDA.

In a fifth separate aspect of the present invention, an internalcombustion engine includes a variable volume internal combustion enginewith an intake. The internal combustion engine further includes an airdensity sensor for producing an output signal as a function of thedensity of the air in the intake. A display displays the output signalsin units reflecting engine performance.

The internal combustion engine may include a plurality of air densitysensors, may include at least one density changing device and mayinclude the sensing of other engine operating conditions to augmentaccurate determination of performance levels.

In a sixth separate aspect of the present invention, a method fordisplaying the performance level of an internal combustion engineincludes sensing the density of the air flowing in the intake andgenerating a signal which is a function of the density sensed. Thesignal is converted to units indicative of internal combustion engineperformance and presented on a display.

In a seventh separate aspect of the present invention, a plurality ofdensity sensors are contemplated for placement at locations relative toone or more density changing devices. Signals are generated at least asa function of density at the sensor locations and calculations areperformed to provide a display of performance level of the internalcombustion engine. Sensing of additional operating conditions of theinternal combustion engine are also contemplated.

In an eighth separate aspect of the present invention, sensors inaddition to density sensors are contemplated to augment indication ofperformance. Sensors for engine speed, humidity, flow rate and powerdemand are contemplated.

In a ninth separate aspect of the present invention, any of theforegoing aspects are contemplated to be combined to greater advantage.

Accordingly, it is an object of the present invention to provideimproved performance sensing systems and methods. Other and furtherobjects and advantages will appear hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an internal combustion engine with an“all-mechanical” density sensor.

FIG. 2 is a schematic view of an internal combustion engine with twodensity increasing devices in series in the intake, with electronicsensors, a discrete processor, and a display.

FIG. 3 is a schematic view of an internal combustion engine with twodensity increasing devices in series in the intake with electronicsensors and a dash mounted digital processor providing operator input,display, and processing functions.

FIG. 4 is a schematic view of an internal combustion engine with twodensity increasing devices in series in the intake with digital data bustype electronic sensors, and a dash mounted digital processor.

FIG. 5 is a schematic view of an internal combustion engine with threedensity increasing devices in series with sensors in between themultiple stages and an engine control module.

FIG. 6 is a schematic view and logic diagram of a dash mounted PDAinterfacing with an engine control module diagnostic data output port.

FIG. 7 is a schematic view and logic diagram of a dash mounted PDAinterfacing with a digital data bus.

FIG. 8 is a schematic view and logic diagram of a dash mounted PDAinterfacing with conventional analog sensors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments, systems of apparatus and method, sense anddetermine the density of the air at one or more strategic locations inthe intake system of an internal combustion engine, and present thisinformation to the operator in useful forms indicative of internalcombustion engine performance including power and, more directly, thatof the intake system. Various embodiments can include predictions ofengine power levels based on density gains or losses, and present thisdata to the operator in real time. Power is predicted by establishingpower at a first density and speed and then estimating power throughchanges in density brought about by changes in density changing devices.Multiple reference points with established power data assist in thisprediction. Empirical functions can then be developed, specific to eachtype of engine, to predict power based on changes in density with enginecomponents other than the density changing devices remaining constant.Other engine parameters can be sensed and provided to the display toaccommodate for other power impacting variables.

The systems accommodate various density changing devices employed on theengine. “Density changing devices” are here defined as a category ofdevices that have an effect on the intake air density by eitherincreasing or decreasing it. This category includes devices thatincrease the density of the air by compressing it, like a superchargeror turbocharger, devices that increase the density of the air by coolingit, like charge air coolers, and conversely, devices that decrease thedensity by lowering the pressure, either intentionally such as by athrottle valve or unintentionally such as through an improper or spentair filter.

The systems are compatible with sensors capable of determining thedensity directly, indirectly, or in combination. The systems areindependent of internal combustion engine type. However, if enhancedreadings for predicting power levels are provided, additional sensorsmay be required or advantageous. For example, fuel settings for CIengines and engine speed allow calculation of power for internalcombustion engines that operate at more than one speed.

A number of air density sensors are disclosed. The term “density sensor”is used here regardless of the mechanism by which the resulting densityis derived. As will be disclosed, known mechanical sensors as well asseparate pressure and temperature gauges with known integrating elementsand computers in the form of PDAs to achieve density readings arecontemplated to fall within the scope of this term.

Certain embodiments are shown to use commercially available PersonalDigital Assistants, or PDA's, or similar small computing device, thathas a program loaded into its memory to perform the calculation stepsrequired to convert the raw sensor data to the units selected by theoperator. A PDA can also serve as an input device to allow the operatorto select the data to be displayed, and the display format. Finally, aPDA can serve as the display to show the results to the operator in thedisplay format chosen. The mass production of PDA's commonly makes themavailable at a lower cost than a display for building a dedicated gaugein lower volumes. Currently available PDA's can employ interfacingcircuitry to communicate with common sensors and engine data busses. AsPDA's and sensors become more advanced in the future, the need for theseintermediate interfacing circuits will likely be eliminated, simplifyingthe implementation of these systems.

A variety of density changing devices and sensor types are intermixed inthe following figures and embodiment descriptions. This variety isintended to demonstrate the flexibility of the systems in a variety ofapplications, and to illustrate the operation of the systems in a fewtypical installations. These features are essentially interchangeable,and the figures and descriptions should not be construed to limit thecombination to those few shown herein for the sake of brevity, but todemonstrate the flexibility of these systems.

The simplest embodiment is illustrated schematically in FIG. 1 with aninternal combustion engine 10 equipped with an intake from the aircleaner 80 to the engine 10. The intake includes a density changingdevice in the form of a supercharger 20. The intake air 82 is drawnthrough the air cleaner 80 and is compressed by the 1st stage intake aircompressor 22 of the supercharger 20. the compressed air then travelsinto the intake manifold 30 and then into the engine 10. The densitylevel in the intake manifold 30 can be controlled via a throttle valve.This can take the form of a compressor inlet throttle 33 disposed priorto the supercharger 20, or an intake manifold throttle 34 disposed afterthe supercharger 20.

A mechanical air density sensor 40 is used to determine the density ofthe air in the intake manifold 30. The mechanical density sensor 40includes a bellows 38 which has been evacuated and then partially filledwith a reference gas such as nitrogen 39 in predetermined quantity.

Locating the mechanical density sensor 40 within the intake manifold 30so that it is exposed to the intake airflow allows the gas within thebellows to assume the same temperature as the airflow. The combinationof pressure within the intake manifold 30 and the transferredtemperature cause a resulting pressure within the bellows 38 that can becalibrated to indicate the density of the intake manifold 30. Thepressure provides an output signal which is in communication with amechanical pressure sensor that provides a display 53. The display facecan be marked in units to read density directly, density gain or lossfrom a defined reference, or to indicate engine performance or powerlevel as a function of density.

This embodiment would be used on engines that had little or noelectronic controls, or even applications devoid of an electricalsystem. (i.e. compression ignition) It would also be entirely immune tosevere electrical interference, including even electromagnetic pulseeffects when used in nuclear hardened military applications. Since thissystem cannot sense the fuel setting of a CI engine, it would onlypredict the maximum possible power assuming a full fuel setting,however, this is commonly the operating point of most interest. Likewiseany power comparisons would only be valid for the same engine speed.Look-up tables and functions empirically determined can be incorporatedto provide more versatile comparisons at various engine speeds andaccelerator settings.

FIG. 2 shows a similar schematic with the addition of a second densitychanging device, a charge air cooler 66 in series with the supercharger20. The charge air cooler cools the airflow, and hence increases thedensity after it exits the 1st stage intake air compressor 22 on its wayto the intake manifold 30 through an intake manifold throttle 34.

This embodiment uses electrical sensors in close mutual proximity tosense the pressure and temperature values at various points throughoutthe system to generate an output as a function of density at selectedlocations. An intake air ambient density sensor includes a temperaturesensor 48 and a pressure sensor 49 to measure incoming conditions to theintake. The air is then compressed and read again by the 1st stagedensity sensor including a temperature sensor 46 and a pressure sensor47. The air is read a third time after the air is cooled by the chargeair cooler 66 where the resulting density increase is measured in theintake manifold by combined data from the intake manifold temperaturesensor 42 and the intake manifold pressure sensor 43. This embodimentwould also work if a single sensor capable of sensing density directlywere substituted for the pair of discrete temperature and pressuresensors at each location depicted in FIG. 2.

Each pair of sensors generates an electrical output signal as a functionof density and including pressure and temperature components which arecommunicated individually through a wiring harness 54 to a display. Aconverter operating as a density gauge processor unit 50 converts thediscrete temperature and pressure sensor signals to density and/or poweroutput, or density and/or power output gain or loss values, and thenoutputs this data to a display panel 53. The operator can provide datainput to the processor 50, via the position of the selector switch 51,which determines which data and presentation format, or units, theoperator wishes to view.

This embodiment would lend itself to retrofitting an engine that had nooriginal equipment instrumentation, as well as applications where adensity-changing device is being retrofitted as a performance upgrade.In such cases, the processor portion of the system 50 could incorporatean add-on engine processor that controlled the retrofit performanceupgrade system, which commonly requires data from manifold pressure andtemperature sensors to modify the amount of fuel provided, and wouldthereby simplify the implementation of the retrofitted system.

FIGS. 3 and 4 show schematics of two systems of indicating performanceon an internal combustion engine 10 similar to FIG. 2, except that theengine depicted employs a 1st stage turbocharger 21 with a 1st stageintake air compressor 22 in place of the mechanically drivensupercharger 20 shown in FIG. 2. The supercharger of FIG. 2 derives thepower needed to drive the 1st stage intake air compressor 22 from theinternal combustion engine 10 through a mechanical link. Theturbocharger in FIGS. 3 and 4 derives the power needed for the 1st stageintake air compressor 22 from the energy in the internal combustionengine exhaust by running the exhaust through a turbine 24.

The power delivered to the compressor 22 and, therefore, the compressoroutput pressure is controlled by selectively bypassing some exhaust flowaround the turbocharger turbine through a wastegate valve 27. Pressurelevels in the intake manifold 30 are sensed through a wastegate pressureline 28, which provides a feedback signal to control the position of thewastegate valve 27 to maintain a preselected pressure level in theintake manifold 30.

Both systems provide air density sensors by locating sensors in closeproximity for temperature and pressure at the inlet (sensors 48, 49 inFIG. 3 and 98, 99 in FIG. 4), after the 1st stage compressor 22 butbefore the charge air cooler 66 (44, 45 in FIG. 3 and 96, 97 in FIG. 4)and then again in the intake manifold (42, 43 in FIG. 3 and 92, 93 inFIG. 4) with each density sensor providing an output signal oftemperature and pressure data as a function of density. A analogthrottle position sensor (41) or similar device captures the power levelrequested by the operator needed to calculate power at less than fullload conditions for CI applications. The engine speed data for assistingin the calculation of power at various speeds can be sensed from theignition (SI), the fuel injection (electronic controlled CI), a halleffect sensor, a crankshaft position sensor, a camshaft position sensor,an alternator, a tach generator, and similar means appropriate to theengine type. A speed sensor feed 124 provides the speed signal to thedisplay in FIG. 3 and the engine control unit (ECU) 52 is a speed signalsource in FIG. 4.

The difference in these systems is that the system of FIG. 3 produces ananalog voltage or current output that has a separate wire for eachsensor in the harness 54 and multichannel data acquisition circuitry 125illustrated in FIG. 8 to convert these analog signals to a digital formcompatible with the converter and digital processor inside the PDA 58.

FIG. 4 depicts digital air density sensors by locating pairs oftemperature and pressure sensors 92, 93, 94, 95, 98, 99 in closeproximity for temperature and pressure that can communicate with theengine ECU 52 over a data bus 60, and do not have discreet wires foreach sensor, multiplexing, or analog to digital conversion. Thesedigital data buses 60, however, typically operate at different signallevels than data processors to increase their immunity to outsideelectrical interference, and still has an interface circuit tocommunicate with current PDA designs. In some applications this willallow the use of existing sensors that may be present on modernelectronic controlled engines to provide the needed data. The powerlevel requested by the operator and engine speed can also be obtainedfrom the ECU 52, eliminating the need for reading the acceleratorposition or a speed sensor.

FIG. 5 shows a schematic of an internal combustion engine 10 with anadditional 2nd stage turbocharger 71 added in series to the 1st stageturbocharger 21. An additional digital air density sensor is provided bylocating a pair of sensors 46 and 47 in the duct 78 between thedischarge of the 1st stage air compressor 22 and the inlet to the 2^(nd)stage air compressor 72. A temperature sensor 67 senses the coolingmedium 69 entering the charge air cooler 66. This figure depicts anembodiment where the analog sensors are read directly by the enginecontrol processor 52, and the density is determined for display fromdata obtained from the diagnostic port on the engine processor 52through an OBD II (or similar) data communications link. 61 Thisembodiment would also lend itself to being incorporated into a retrofitsystem to add an additional density-changing device as a performanceupgrade. In such cases, the processor function of the density gaugesystem could be incorporated into a retrofitted engine control processor52, making the gauge system an integral part of the upgrade package. Inthis embodiment the engine speed and the power level requested by theoperator can be obtained from the ECU 52 directly, eliminating the needfor reading the engine speed or the accelerator position sensor 41 forthe purposes of calculating CI engine power at part load.

FIGS. 3 through 8 also depict 3 common variations on the preferredembodiment of the system utilizing a PDA 58, or a similar small computercapable of providing the operator input, converter and processorfunctions, memory, and the display for the system. The PDA 58 is mountedin a PDA cradle and interface 59, and is mounted to the vehicledashboard 55 for easy viewing and operation by the vehicle operator. Thecradle can interface with the PDA 58 via the PDA's infrared interfaceport 56 through the PDA cradle's corresponding infrared interface port57 as seen in FIG. 8. This reduces the sensitivity to the motion of thePDA relative to the cradle that can be induced by vibration from thevehicle. This relative motion between the cradle and the PDA candeteriorate the quality of the electrical connection at the base of thePDA where it plugs into the cradle with mechanical contacts that canwear as a result of the vibration.

The system is intended to be a permanently installed gauge, although thecradle allows the PDA itself to be easily removed and used as a normallyfunctioning PDA when the vehicle is not in use. This also allows theneeded program to operate the system to be installed initially, and thento be easily updated by the user as new versions of the program becomeavailable. These programs can be downloaded from a floppy disk, CD, orFlash drive included with the system, or downloaded directly from themanufacturer's website. The programs would initially be downloaded intoa personal computer, and then downloaded into the PDA's memory using thesame personal computer to PDA interface hardware that was originallysupplied with the PDA for this purpose. Depending on the communicationcapability of the PDA chosen, some of the logic block functions shown inthe following figures that interface sensor data to the PDA may beperformed within the PDA. In all cases, the PDA will have beenpre-programmed to start automatically upon power up of the internalcombustion engine, request which data the operator wants to see, readthe corresponding sensors, calculate the requested values, and thenpresent it to the operator on the PDA screen in the visual displayformat selected.

FIG. 6 shows a block diagram of the PDA adapter cradle used with anoverall system as depicted in FIG. 5 where the system reads the data itneeds from the engine processor 52. The first block 110 would convertthe electrical interface format used by the engine processor (e.g.,OBD-II, 61 etc.) to a logic level. The next block is a micro controller105 that would convert the data format to one compatible with the PDA. Alogic-to-PDA interface circuit 100 would then convert themicrocontroller electronic output logic level to one compatible with thePDA. This version communicates to the PDA through a PDA data portelectrical plug with mechanical contacts 115.

FIG. 7 shows a block diagram of the PDA adapter cradle used with anoverall system as depicted in FIG. 4, where the system reads the data itneeds from the digital sensors through the engine's digital data bus 60.This data bus could also be retrofitted if any or all of theadvantageously included sensors were not originally present on theengine. The first block 120 converts the digital sensor data bus signalsto a logic level the microcontroller can read. (e.g. a CAN bustransceiver) The next block is a micro controller 105 that converts thedata format to one compatible with the PDA. A logic-to-PDA interfacecircuit 100 would then convert the microcontroller electronic outputlogic level to one compatible with the PDA. This embodiment communicatesto the PDA through a PDA data port electrical plug with mechanicalcontacts 115.

FIG. 8 shows a block diagram of the PDA adapter cradle used with anoverall system as depicted in FIG. 3 where the system reads the data itneeds from analog sensors with a multichannel analog to digital dataacquisition circuit 125 through a wiring harness 54. The multichannelanalog to digital data acquisition circuit 125 then feeds themicrocontroller 105 that then sends the data to the PDA 58 through thePDA cradle side infrared interface port 57 to the PDA's infraredinterface port 56. This embodiment demonstrates that a system withmultiple density increasing devices would further benefit from theability to display any combination of the power levels, the absolutedensity, the gain or loss in density, the temperature, or the pressureat any point in the system, as well as the drop or increase in thesevalues across each density changing device.

The equations for converting the raw sensor data to actual temperature,pressure, and density values depend on the type of sensor used. Theseequations are typically industry standard, or obtained from the sensormanufacturer. The density of dry air measured at a standard temperatureand pressure is generally considered to be 1.2 kg/m³ (0.075 lb/ft³)measured at 21.1 C (70 F) and 101.3 Pa (29.92 in. HgA). To calculate thedensity at other temperatures and pressures, multiply the density by theratios (actual P air/101.3)*((21.1+273.1)/(actual T air+273.1)) whereTemp=C, Press=Pa. The density ratio is the density under currentconditions divided by the density at a reference condition. This ratiois dimensionless.

The percentage density gain or loss would commonly be calculated in oneof two ways. One method, the reference point is defined as idle, or“zero” power, and full power without a boosting device would approach100%. This would always register as a gain or be “positive”. Boostingthe power above this would provide a power gain of over 100%. Thisapproach would commonly be used in aircraft, or similar applicationswhere the ambient reference conditions change frequently, and where aquickly interpreted “safe maximum power” reference independent of thecurrent ambient conditions is most critical to the operator. The secondapproach would set the reference conditions equal to be 100% power, andany gain or loss from these conditions would be indicated as positive ornegative. This would be useful where changes from a reference point wereimportant, such as testing the performance change resulting from anintentional change in the system. Conversely, this format would alsoquickly alert the operator to an unintentional performance change, suchas might result from an impending failure in part of the system.

The simplest approximation of engine power change for a spark ignition(SI) engine using density gain or loss is the density percentagemultiplied by the power produced at the reference density at a givenengine speed. This estimate will be low because the losses fromfriction, thermal, and pumping losses do not increase proportionatelywith density, so the power increase will actually be greater thancalculated. A more accurate method would be to multiply the density bythe power at the reference density without the losses, then subtract thelosses from the new value. The losses vary from one internal combustionengine to another, and could be modeled for each engine using industrystandard methods (SAE J13490, etc.) for internal combustion enginemeasurements. This calculation assumes that the engine control systemwill change the amount of fuel being injected as density changes tomaintain the narrow range of air/fuel ratio required by a SI engine. Agauge application with a multi speed engine would also use a speed inputto calculate power.

Compression Ignition (CI) or Diesel engines can run at a wider range ofair/fuel ratios than SI engines, and this must be taken into accountwhen calculating power. If sufficient air is present to burn all of thefuel being supplied, increasing the intake air density will not causeany corresponding increase in power. Power can still be calculated, butsensing the amount of fuel being supplied is required. The fuel rate canbe determined by sensing the throttle position sensor, 41 sensing theinjector pulse width, sensing the fuel injection pump rack position,obtaining the fueling rate information from the engine control unit 51or a power train control unit through the data bus, 60 or the OBD IIcommunications link 61, etc. As is the case with an SI engine, a gaugefor a multi speed CI engine would also need a speed input to calculatethe engine power at various engine speeds.

Systems that are equipped with a compressor, like a supercharger orturbocharger, could be monitored for temperature and pressure rise, andfrom this data the compressor efficiency could be calculated anddisplayed. Compressor efficiency for air=T in [((P out/Pin)^(0.286))−1]/(T out−T in). See also SAE J1826. Similarly, systemsequipped with a charge air cooler, or similar heat exchanger could bemonitored for the performance of the heat exchanger, and this valuecalculated and displayed. This would require one additional temperaturesensor in the flow of the cooling medium (air, water, coolant, etc,) tocalculate the heat exchanger performance. Heat exchangereffectiveness=(T in−T out)/(T in−T cooling medium). See also SAE J1148.The compressor and charge cooler performance information would be usefulfor assessing the effect of component changes, but should not changeduring normal operation. These values would therefore provide animmediate indication of a malfunction if they did change.

The values displayed can be fixed during manufacture, or be changeableby the operator. It could be set change automatically from one to thenext in sequence, again either preset, or as selected by the operator.The display could also be programmed to change automatically like analarm, to display a value that exceeds a desired range to alert theoperator to the condition that has either been preset, or set by theoperator. The displayed information can be used by the operator toassist in internal combustion engine output control, as well asmonitoring performance of each component in the system, and the overallsystem performance in real time. The operator would have the option toselect which data or combination of data to view depending on the areaof interest at the time.

Humidity can be monitored. It is the only significant natural variablein the constituent mixture as applied to conventionally employedengines. As humidity affects power, it can be factored in regardingpower estimates, again through empirically developed functionsparticular to each engine or type of engine. The humidity typically doesnot affect the Ideal Gas formula. Therefore, where the power estimate isintended as a comparative measurement of a change in performance of theintake system or density changing devices therein, humidity is notconsequential. The humidity reading from a sensor 126, as shown in FIG.2, may be used where appropriate in this context. The power output canbe modified to account for humidity by using a function of humidity tovary the density as applied to the predicted power output. Electronichumidity sensors are contemplated in an engine environment.

Another engine parameter which provides information useable forperformance indications is flow rate of air through the engine. Changesin the engine valve setting or in the exhaust side of the engine canimpact flow. As flow impacts the amount of oxygen available forcombustion, changes in performance can be impacted by flow as well asdensity. The sensor 126, as shown in FIG. 2, can represent a flow meterused for indicating changes in flow impacting performance.

The foregoing disclosure deals with the efficiency of the intake side ofthe engine. To achieve power estimates, an assumption is made that theremainder of the engine, from the intake valves and ignition through themuffler, remains constant. This assumption is quite valid unless changesare made which are not part of the intake up to the intake valves. Onesuch change that occurs during operation of certain engines isvariations in effective engine displacement. Fuel economy for amulti-cylinder internal combustion engine can be improved bydeactivating some of the engine cylinders under certain operatingconditions. Reducing the number of operating cylinders reduces theeffective displacement of the engine. This is sometimes referred to inthe art as a variable displacement engine.

Depending upon the particular configuration of the variable displacementengine, one or more cylinders may be selectively deactivated by acontroller. The controller generates a signal which is used to send asignal to the gauge processor to indicate the current displacement. Thegauge processor in this configuration creates a displacement factor toadjust the performance calculation. This factor can be the actualdisplacement divided by maximum displacement or can be empiricallydetermined for specific engines is the effect is found not to be linear.

FIG. 4 can be used to depict a variable displacement engine 10 where thedisplacement is controlled by selectively deactivating cylinders undercontrol of the ECU 52. The ECU 52 would provide a variable displacementsignal indicative of the displacement through the data bus 60 to the PDA58 to allow the actual displacement to be incorporated into theperformance calculations. The data bus 60 may also actuate the variousengine components that effect a cylinder shutdown. The PDA 58 canmonitor these engine cylinder shutdown commands via the data bus 60.

Thus, measurement and display of engine performance as a function ofdensity as method and apparatus are disclosed. While embodiments andapplications of this invention have been shown and described, it wouldbe apparent to those skilled in the art that many more modifications arepossible without departing from the inventive concepts herein. Theinvention, therefore is not to be restricted except in the spirit of theappended claims.

1. An internal combustion engine comprising a variable volume internalcombustion engine including an intake with air flow therethrough; an airdensity sensor disposed in the intake and producing an output signalthat is a function of the density of the air in the intake; a display incommunication with the air density sensor displaying the output signalin units selected from a group consisting of density, density divided bya predetermined value, percent density gain or loss, power output, poweroutput divided by a predetermined value and power output gain or loss.2. The internal combustion engine of claim 1, the air density sensorincluding a gas tight flexible container disposed within the intake, agas disposed within the flexible container, a predetermined quantity ofwhich is selected to produce a pressure that is a function of thedensity of the air in the intake, a pressure sensor sensing the pressureof the gas within the flexible container and generating the outputsignal.
 3. The internal combustion engine of claim 1, the output signalbeing an electrical signal, the display including a converter incommunication with the air density sensor converting the output signalinto the units selected from the said group and a display panel incommunication with the converter to display the output signal in theunits selected from the said group.
 4. The internal combustion engine ofclaim 3, the converter including a digital processor having logic toconvert the output signal into more than one of the units selected fromthe said group.
 5. The internal combustion engine of claim 4, theconverter being a PDA.
 6. The internal combustion engine of claim 3, theair density sensor including a pressure sensor producing a pressuresignal and a temperature sensor producing a temperature signal, thepressure sensor and the temperature sensor being in close proximity inthe intake, the pressure signal and the temperature signal being theoutput signal.
 7. The internal combustion engine of claim 3 furthercomprising a humidity sensor in communication with the display andincluding a humidity signal that is a function of the humidity in theinlet.
 8. The internal combustion engine of claim 3, the variable volumeinternal combustion engine being a variable displacement internalcombustion engine including a ECU generating a variable displacementsignal in communication with the display and employed by the display. 9.The internal combustion engine of claim 1 further comprising a pluralityof said air density sensors producing a plurality of output signals,respectively, the intake including at least one density changing device,at least one of the air density sensors being upstream of the at leastone density changing devices and at least another of the air densitysensors being downstream of the at least one density changing devices.10. The internal combustion engine of claim 9, the at least one densitychanging device being a compressor, the output signals being electricalsignals, the display including a converter in communication with the airdensity sensors converting the output signals into the units selectedfrom the said group and further providing differences between outputsignals in the units selected from the said group and a display panel incommunication with the converter to display the converted outputsignals.
 11. The internal combustion engine of claim 10, the at leastone density changing device being a compressor and a charge air cooler.12. The internal combustion engine of claim 10 further comprisingadditional sensors of internal combustion engine operating conditionsselected from a group consisting of fuel rate being supplied to theinternal combustion engine, power level requested by an operator, flowrate of air through the engine and internal combustion engine speed. 13.A system for indicating the performance of an internal combustion enginehaving an intake with air flow therethrough, comprising an air densitysensor disposed in the intake and producing an output signal that is afunction of the density of the air in the intake; a display incommunication with the air density sensor displaying the output signalin units selected from a group consisting of density, density divided bya predetermined value, percent density gain or loss, power output, poweroutput divided by a predetermined value and power output gain or loss.14. The system of claim 13, the air density sensor including a gas tightflexible container disposed within the intake, a gas disposed within theflexible container, a predetermined quantity of which is selected toproduce a pressure that is a function of the density of the air in theintake, a pressure sensor sensing the pressure of the gas within theflexible container and generating the output signal.
 15. The system ofclaim 14, the display including a gauge attached to the pressure sensorincluding a face labeled with a scale to display the output signal ofthe pressure sensor in units selected from a group consisting ofdensity, density divided by a predetermined value, percent density gainor loss, power output, power output divided by a predetermined value andpower output gain or loss.
 16. The system of claim 13, the output signalbeing an electrical signal; the display including a converter incommunication with the air density sensor converting the output signalinto the units selected from the said group and a display panel incommunication with the converter to display the output signal in theunits selected from the said group.
 17. The system of claim 16, theconverter including a digital processor having logic to convert theoutput signal into more than one of the units selected from the saidgroup.
 18. The system of claim 17, the digital processor being a PDA.19. The system of claim 16, the air density sensor including a pressuresensor producing a pressure signal and a temperature sensor producing atemperature signal, the pressure signal and the temperature signal beingthe output signal.
 20. The system of claim 16 further comprising ahumidity sensor in communication with the display and including ahumidity signal that is a function of the humidity in the inlet.
 21. Amethod for displaying the performance level of an internal combustionengine having an intake, comprising sensing the density of the airflowing in the intake; generating a signal that is a function of thedensity sensed; converting the density signal into the units to bedisplayed, selected from a group consisting of density, density dividedby a predetermined value, percent density gain or loss, power output,power output divided by a predetermined value and power output gain orloss; presenting the converted density signal on a display.
 22. A methodfor displaying the performance level of an internal combustion enginehaving an intake, comprising sensing the density of the airflow enteringthe internal combustion engine at locations selected from a groupconsisting of intake air flow in an intake manifold, intake air flowupstream of a density changing device, intake air flow downstream of adensity changing device, and the intake air flow in between any twodensity changing devices; generating signals that are a function of atleast the density at the sensor locations; calculating any combinationof internal combustion engine performance based upon the signalsgenerated using predetermined formulas for the density and the poweroutput of the internal combustion engine, the values calculated beingselected from a group consisting of the density, the difference betweenany two densities, the density divided by a predetermined value, percentdensity gain or loss, power output, percent power output divided by apredetermined value, percent power gain of loss, the compressorefficiency, the charge air cooler effectiveness; presenting theconverted density signal on a display.
 23. The method of claim 22further comprising sensing additional operating conditions selected froma group consisting of fuel rate being supplied to the internalcombustion engine, power level requested by an operator, air flow ratethrough the engine and internal combustion engine speed; correcting theinternal combustion engine performance calculated to account for theadditional sensed data.
 24. The method of claim 22 further comprisingsensing the humidity of the airflow; generating signals that are afunction of humidity of the airflow, calculating power output includingmodifying density as a function of humidity of the airflow.
 25. Themethod of claim 22 further comprising sensing a variable displacementsignal; correcting the internal combustion engine performance calculatedto account for the variable displacement signal.